I'm a 22 y/o male with a jumbled lifting history, 6'3", and between 180-190 lb.

Exercise goals are to build muscle; both strength and endurance.

Lifting history:
So I initially tried lifting around 18 with guidance from bodybuilding,com, I probably changed my routine up every three months or so.

A year and a half ago I discovered I had scapula winging and shoulder instability, and basically quit all lifting to work on shoulder mobility/rehab (sleeper stretch, pec-minor stretch, external rotation with band, lower trap exercise with band, serratus anterior punching exercise with band) and eventually leg mobility so I could start squatting.

Within about 3 months I moved up to doing lat pulldowns, pushups (emphasizing the top press motion), cable-assisted pistol squats, and slightly varied forms of the ext. rot. and low-trap band exercises. I found pistol squats with a machine difficult to progress with (relatively a lot of counterweight to be holding onto), so I began to do barbell back squats to see if I could progress my leg strength further before going back to pistol squats. I began at bar weight and as I moved up in weight I found pain due to tennis elbow in one of my arms, so I decided to stop with back squats and now I am doing landmine squats.

-My first question: is it is safe to work on developing my chest with bench press or chest dips in addition to push-ups, or may this over activate my pecs taking away from progress I have made with my back exercises?

-My second question: I read that front squats are an auxiliary movement, while back squats are a basic movement; how can I compensate for this in my routine?

-My third question: I wanted to add some exercises to my current routine, and I set it up for two identical upper/two identical lower workout days a week.

To make this a long-term program, do these exercises/sets/reps make sense for progress? Should I have light/heavy days for the basic movements I want to add in, and if so what would the weight and set/rep ranges be?

also, if I were to switch back to cable assisted pistol squats, I was doing 3x15 before (really hard and time consuming), but would a 5x5 for cable assisted pistol squats work better than front squats?

I know this is really long, so if you manage to read, understand, and give me your input on all of this thank you ahead of time!